1. Field of the Invention
The present invention is related to the use of instruments for guiding preparation of a knee for installation of an implant during an arthroplasty, and in particular, to the use of ligaments around the knee and other anatomical features to position the guide instruments and making reference cuts to the tibia and the femur.
2. Description of Related Art
During a knee arthroplasty, a surgeon typically must gain access to the knee joint in order to perform resections of existing bone and cartilage so as to shape the tibia and femur to fit mating surfaces of the implant. Some arthroplasty procedures seek to minimize the invasiveness of the approach to the knee joint by minimizing the size of the incision in the surrounding soft tissue structure of the knee and the patella. Preserving the soft tissue structure also preserves some of the support provided by these tissues. However, preserving the soft tissues surrounding the knee can be difficult at times due to the need to firmly support the resection guides relative to the bone of the tibia and the femur.
The manner in which the natural knee joint performs is largely affected by the tension in the collateral ligaments of the knee, as well as by the alignment of the articular surfaces of the knee joint relative to the collateral ligaments. In the natural knee joint, the plane of the articular surfaces of the femur and the tibia bisects the collateral ligaments at an optimal, physiological position. This optimal, physiological position enables the knee joint to flex and extend in a balanced and properly aligned manner. Exemplary arthroplasty procedures resection the femur and the tibia, yet preserve the optimal, physiological position of the knee joint when fitted with a prosthesis.
Preservation of the ligamentous and other soft tissue structures around the knee can provide a reference point for accurately positioning the tibial and femoral components of the knee implant, in particular when said structure is in tensed or otherwise loaded condition. For example, ligament tensions can be used to guide placement of resection guides. Conversely, preservation of the soft tissue structures requires balancing of the forces exerted by the soft tissues to promote normal kinematics in the knee and normal patellar tracking. Therefore, ligament forces can play a significant role in restoring normal function to a knee. Generally, therefore, reductions in the invasiveness of the knee arthroplasty procedure combined with improvements in the positioning and installation of knee components can result in a better overall surgical outcome for the patient.
It would therefore be advantageous to have instrumentation for guiding resection of the femur, tibia and other structures in the knee during a knee arthroplasty that works well with minimally invasive approaches to the tibia and femur. It would be further advantageous if the instrumentation assisted the balancing of forces between the knee implant components and the preserved ligamentous and soft tissue structures for improved function of the knee implant. Also, it would be advantageous to have instrumentation for guiding resection that uses the ligamentous structure of the knee to guide placement of the instrumentation and the resulting optimal alignment and physiological positioning of the knee prosthesis.